LCDs are widely used in various electronic information products, such as notebooks, personal digital assistants, video cameras, and the like. A conventional LCD usually employs a liquid crystal panel to display images. The liquid crystal panel contains a layer of liquid crystal for generating images. However, the liquid crystal does not generate light itself. Therefore a light source such as a backlight module or ambient light is needed to illuminate the liquid crystal in the liquid crystal panel.
During operation of a conventional LCD, invariable driving voltage signals are stably provided to light sources of a backlight module. This enables the light sources to continuously emit light beams to the liquid crystal panel. Liquid crystal molecules in the liquid crystal panel tilt to corresponding angles according to display signals applied to pixels units that span the layer of liquid crystal. Therefore the amount of light beams transmitting through the liquid crystal molecules at each pixel unit is controlled. The aggregation of light beams transmitting through all the pixel units simultaneously constitutes an image displayed on a screen of the liquid crystal panel.
When the LCD displays a dark image, a so-called gray level of the displayed image is relative low. Only a small amount of light beams are needed to generate a dark image. However, because the driving voltage signals provided to the light sources are invariable, therefore the amount of light beams emitted by the light sources is also invariable. In this circumstance, many or most of the light beams may be unused and simply wasted. That is, the light utilization efficiency of the LCD is low. In addition, when the LCD displays a black image, the liquid crystal molecules at the pixel units of the liquid crystal panel may be influenced by ambient interfering electrical signals. When this happens, the liquid crystal molecules at the pixel units may not be capable of completely blocking transmission of all the light beams incident thereon. This is liable to induce a so-called light leakage phenomenon, whereby a contrast ratio of the LCD may become unsatisfactory.
What is needed is to provide an LCD and a method for driving the LCD that can overcome the above-described deficiencies.